With the development of technologies, people are no longer content with inactively watching a program on a TV or computer, rather, they prefer to control the playing of the program, for example, to skip the advertisement using “fast forward” or repeatedly watch an exciting scene using “rewind”. Such kind of media applications that involve interactive control from the users are referred to as interactive media services.
Currently, interactive media services are widely used, such as the content-on-demand application in digital TV which allows the user to arbitrarily control the playing procedure, and e-learning application which allows a student to review a certain part of what the teacher just taught at any time.
In the interactive media service, the user is allowed to perform user interactive control operations such as pause, fast forward, rewind, etc. Currently, these interactive controls are carried out through a Real Time Stream Protocol (RTSP), which defines a message mechanism and data packet for the interactive controls between a media sender and receiver. Generally, the media receiver is a terminal, such as a television, a computer, a mobile phone, a PDA, etc., and the media sender is a data source for storing the media, usually a media server.
For the media sender and receiver to transmit an interactive control signaling, a channel for delivering the signaling, i.e., an RTSP connection, must be established. The connection can be established using either Transport Control Protocol (TCP) or User Datagram Protocol (UDP), and the default port number is 554. Meanwhile, a channel for delivering a media needs to be set up, which is typically a Real-time Transport Protocol (RTP) connection. The RTP connection is generally established through UDP. In a conventional network environment, the media sender and receiver establish the RTSP connection first, and then negotiate the address for RTP connection using a SETUP message over the RTSP connection. When the negotiation on the address is finished, the media receiver notifies through a PLAY message the media sender to start playing the media stream.
IP Multimedia Subsystem (IMS) uses an IP grouping domain as a carrier channel for controlling signaling and media delivery, and uses Session Initiation Protocol (SIP) as a call control signaling, thereby separating service management, session control and carrier access from each other.
The IMS network architecture having above separate feature provides necessary conditions for fast deployment and uniform control of various services, which include not only session services but also media services. In the IMS network environment, uniform service management is realized through an application server. In the media service applications, various specific media applications can be deployed in different media application servers, such as a content-on-demand application server, a radio-television application server, etc. Meanwhile, the uniform service control can be conducted by entity and mechanisms at the session control layer.
In the existing system and method for establishing interactive media session, the terminal establishes an RTSP connection with the media server directly and then negotiates an address for RTP connection using the RTSP connection.
In the Next Generation Network (NGN) environment, the carrier function is independent of the control function, and a media server can be disassembled into a media control entity and a media carrier entity. The RTSP connection is established between the terminal and the media carrier entity. However, when the terminal and the media carrier entity negotiate the address for RTP connection over the RTSP connection, the media control entity cannot control the media carrier entity because the negotiation messages do not go through the media control entity.